funcs/func_lock.c

   1 /*
   2  * Asterisk -- An open source telephony toolkit.
   3  *
   4  * Copyright (C) 2007, Tilghman Lesher
   5  *
   6  * Tilghman Lesher <func_lock_2007@the-tilghman.com>
   7  *
   8  * See http://www.asterisk.org for more information about
   9  * the Asterisk project. Please do not directly contact
  10  * any of the maintainers of this project for assistance;
  11  * the project provides a web site, mailing lists and IRC
  12  * channels for your use.
  13  *
  14  * This program is free software, distributed under the terms of
  15  * the GNU General Public License Version 2. See the LICENSE file
  16  * at the top of the source tree.
  17  */
  18
  19 /*! \file
  20  *
  21  * \brief Dialplan mutexes
  22  *
  23  * \author Tilghman Lesher <func_lock_2007@the-tilghman.com>
  24  *
  25  * \ingroup functions
  26  *
  27  */
  28
  29 #include "asterisk.h"
  30
  31 ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
  32
  33 #include "asterisk/lock.h"
  34 #include "asterisk/file.h"
  35 #include "asterisk/channel.h"
  36 #include "asterisk/pbx.h"
  37 #include "asterisk/module.h"
  38 #include "asterisk/linkedlists.h"
  39
  40 /*** DOCUMENTATION
  41         <function name="LOCK" language="en_US">
  42                 <synopsis>
  43                         Attempt to obtain a named mutex.
  44                 </synopsis>
  45                 <syntax>
  46                         <parameter name="lockname" required="true" />
  47                 </syntax>
  48                 <description>
  49                         <para>Attempts to grab a named lock exclusively, and prevents other channels from
  50                         obtaining the same lock.  LOCK will wait for the lock to become available.
  51                         Returns <literal>1</literal> if the lock was obtained or <literal>0</literal> on error.</para>
  52                         <note><para>To avoid the possibility of a deadlock, LOCK will only attempt to
  53                         obtain the lock for 3 seconds if the channel already has another lock.</para></note>
  54                 </description>
  55         </function>
  56         <function name="TRYLOCK" language="en_US">
  57                 <synopsis>
  58                         Attempt to obtain a named mutex.
  59                 </synopsis>
  60                 <syntax>
  61                         <parameter name="lockname" required="true" />
  62                 </syntax>
  63                 <description>
  64                         <para>Attempts to grab a named lock exclusively, and prevents other channels
  65                         from obtaining the same lock.  Returns <literal>1</literal> if the lock was
  66                         available or <literal>0</literal> otherwise.</para>
  67                 </description>
  68         </function>
  69         <function name="UNLOCK" language="en_US">
  70                 <synopsis>
  71                         Unlocks a named mutex.
  72                 </synopsis>
  73                 <syntax>
  74                         <parameter name="lockname" required="true" />
  75                 </syntax>
  76                 <description>
  77                         <para>Unlocks a previously locked mutex. Returns <literal>1</literal> if the channel
  78                         had a lock or <literal>0</literal> otherwise.</para>
  79                         <note><para>It is generally unnecessary to unlock in a hangup routine, as any locks
  80                         held are automatically freed when the channel is destroyed.</para></note>
  81                 </description>
  82         </function>
  83  ***/
  84
  85
  86
  87 static AST_LIST_HEAD_STATIC(locklist, lock_frame);
  88
  89 static void lock_free(void *data);
  90 static int unloading = 0;
  91
  92 static struct ast_datastore_info lock_info = {
  93         .type = "MUTEX",
  94         .destroy = lock_free,
  95 };
  96
  97 struct lock_frame {
  98         AST_LIST_ENTRY(lock_frame) entries;
  99         ast_mutex_t mutex;
 100         /*! count is needed so if a recursive mutex exits early, we know how many times to unlock it. */
 101         unsigned int count;
 102         /*! who owns us */
 103         struct ast_channel *channel;
 104         /*! name of the lock */
 105         char name[0];
 106 };
 107
 108 struct channel_lock_frame {
 109         AST_LIST_ENTRY(channel_lock_frame) list;
 110         /*! Need to save channel pointer here, because during destruction, we won't have it. */
 111         struct ast_channel *channel;
 112         struct lock_frame *lock_frame;
 113 };
 114
 115 static void lock_free(void *data)
 116 {
 117         AST_LIST_HEAD(, channel_lock_frame) *oldlist = data;
 118         struct channel_lock_frame *clframe;
 119         AST_LIST_LOCK(oldlist);
 120         while ((clframe = AST_LIST_REMOVE_HEAD(oldlist, list))) {
 121                 /* Only unlock if we own the lock */
 122                 if (clframe->channel == clframe->lock_frame->channel) {
 123                         clframe->lock_frame->channel = NULL;
 124                         while (clframe->lock_frame->count > 0) {
 125                                 clframe->lock_frame->count--;
 126                                 ast_mutex_unlock(&clframe->lock_frame->mutex);
 127                         }
 128                 }
 129                 ast_free(clframe);
 130         }
 131         AST_LIST_UNLOCK(oldlist);
 132         AST_LIST_HEAD_DESTROY(oldlist);
 133         ast_free(oldlist);
 134 }
 135
 136 static int get_lock(struct ast_channel *chan, char *lockname, int try)
 137 {
 138         struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
 139         struct lock_frame *current;
 140         struct channel_lock_frame *clframe = NULL, *save_clframe = NULL;
 141         AST_LIST_HEAD(, channel_lock_frame) *list;
 142         int res, count_channel_locks = 0;
 143
 144         if (!lock_store) {
 145                 ast_debug(1, "Channel %s has no lock datastore, so we're allocating one.\n", chan->name);
 146                 lock_store = ast_datastore_alloc(&lock_info, NULL);
 147                 if (!lock_store) {
 148                         ast_log(LOG_ERROR, "Unable to allocate new datastore.  No locks will be obtained.\n");
 149                         return -1;
 150                 }
 151
 152                 list = ast_calloc(1, sizeof(*list));
 153                 if (!list) {
 154                         ast_log(LOG_ERROR, "Unable to allocate datastore list head.  %sLOCK will fail.\n", try ? "TRY" : "");
 155                         ast_datastore_free(lock_store);
 156                         return -1;
 157                 }
 158
 159                 lock_store->data = list;
 160                 AST_LIST_HEAD_INIT(list);
 161                 ast_channel_datastore_add(chan, lock_store);
 162         } else
 163                 list = lock_store->data;
 164
 165         /* Lock already exists? */
 166         AST_LIST_LOCK(&locklist);
 167         AST_LIST_TRAVERSE(&locklist, current, entries) {
 168                 if (strcmp(current->name, lockname) == 0) {
 169                         break;
 170                 }
 171         }
 172
 173         if (!current) {
 174                 if (unloading) {
 175                         /* Don't bother */
 176                         AST_LIST_UNLOCK(&locklist);
 177                         return -1;
 178                 }
 179
 180                 /* Create new lock entry */
 181                 current = ast_calloc(1, sizeof(*current) + strlen(lockname) + 1);
 182                 if (!current) {
 183                         AST_LIST_UNLOCK(&locklist);
 184                         return -1;
 185                 }
 186
 187                 strcpy((char *)current + sizeof(*current), lockname);
 188                 ast_mutex_init(&current->mutex);
 189                 AST_LIST_INSERT_TAIL(&locklist, current, entries);
 190         }
 191         AST_LIST_UNLOCK(&locklist);
 192
 193         /* Found lock or created one - now find or create the corresponding link in the channel */
 194         AST_LIST_LOCK(list);
 195         AST_LIST_TRAVERSE(list, clframe, list) {
 196                 if (clframe->lock_frame == current)
 197                         save_clframe = clframe;
 198
 199                 /* Only count mutexes that we currently hold */
 200                 if (clframe->lock_frame->channel == chan)
 201                         count_channel_locks++;
 202         }
 203
 204         if (save_clframe) {
 205                 clframe = save_clframe;
 206         } else {
 207                 if (unloading) {
 208                         /* Don't bother */
 209                         AST_LIST_UNLOCK(list);
 210                         return -1;
 211                 }
 212
 213                 clframe = ast_calloc(1, sizeof(*clframe));
 214                 if (!clframe) {
 215                         ast_log(LOG_ERROR, "Unable to allocate channel lock frame.  %sLOCK will fail.\n", try ? "TRY" : "");
 216                         AST_LIST_UNLOCK(list);
 217                         return -1;
 218                 }
 219
 220                 clframe->lock_frame = current;
 221                 clframe->channel = chan;
 222                 /* Count the lock just created */
 223                 count_channel_locks++;
 224                 AST_LIST_INSERT_TAIL(list, clframe, list);
 225         }
 226         AST_LIST_UNLOCK(list);
 227
 228         /* Okay, we have both frames, so now we need to try to lock the mutex. */
 229         if (count_channel_locks > 1) {
 230                 struct timeval start = ast_tvnow();
 231                 for (;;) {
 232                         if ((res = ast_mutex_trylock(&current->mutex)) == 0)
 233                                 break;
 234                         if (ast_tvdiff_ms(ast_tvnow(), start) > 3000)
 235                                 break; /* bail after 3 seconds of waiting */
 236                         usleep(1);
 237                 }
 238         } else {
 239                 /* If the channel doesn't have any locks so far, then there's no possible deadlock. */
 240                 res = try ? ast_mutex_trylock(&current->mutex) : ast_mutex_lock(&current->mutex);
 241         }
 242
 243         if (res == 0) {
 244                 current->count++;
 245                 current->channel = chan;
 246         }
 247
 248         return res;
 249 }
 250
 251 static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
 252 {
 253         struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
 254         struct channel_lock_frame *clframe;
 255         AST_LIST_HEAD(, channel_lock_frame) *list;
 256
 257         if (!lock_store) {
 258                 ast_log(LOG_WARNING, "No datastore for dialplan locks.  Nothing was ever locked!\n");
 259                 ast_copy_string(buf, "0", len);
 260                 return 0;
 261         }
 262
 263         if (!(list = lock_store->data)) {
 264                 ast_debug(1, "This should NEVER happen\n");
 265                 ast_copy_string(buf, "0", len);
 266                 return 0;
 267         }
 268
 269         /* Find item in the channel list */
 270         AST_LIST_LOCK(list);
 271         AST_LIST_TRAVERSE(list, clframe, list) {
 272                 if (clframe->lock_frame && clframe->lock_frame->channel == chan && strcmp(clframe->lock_frame->name, data) == 0) {
 273                         break;
 274                 }
 275         }
 276         /* We never destroy anything until channel destruction, which will never
 277          * happen while this routine is executing, so we don't need to hold the
 278          * lock beyond this point. */
 279         AST_LIST_UNLOCK(list);
 280
 281         if (!clframe) {
 282                 /* We didn't have this lock in the first place */
 283                 ast_copy_string(buf, "0", len);
 284                 return 0;
 285         }
 286
 287         /* Decrement before we release, because if a channel is waiting on the
 288          * mutex, there's otherwise a race to alter count. */
 289         clframe->lock_frame->count--;
 290         /* If we get another lock, this one shouldn't count against us for deadlock avoidance. */
 291         clframe->lock_frame->channel = NULL;
 292         ast_mutex_unlock(&clframe->lock_frame->mutex);
 293
 294         ast_copy_string(buf, "1", len);
 295         return 0;
 296 }
 297
 298 static int lock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
 299 {
 300         if (chan)
 301                 ast_autoservice_start(chan);
 302
 303         ast_copy_string(buf, get_lock(chan, data, 0) ? "0" : "1", len);
 304
 305         if (chan)
 306                 ast_autoservice_stop(chan);
 307
 308         return 0;
 309 }
 310
 311 static int trylock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
 312 {
 313         if (chan)
 314                 ast_autoservice_start(chan);
 315
 316         ast_copy_string(buf, get_lock(chan, data, 1) ? "0" : "1", len);
 317
 318         if (chan)
 319                 ast_autoservice_stop(chan);
 320
 321         return 0;
 322 }
 323
 324 static struct ast_custom_function lock_function = {
 325         .name = "LOCK",
 326         .read = lock_read,
 327         .read_max = 2,
 328 };
 329
 330 static struct ast_custom_function trylock_function = {
 331         .name = "TRYLOCK",
 332         .read = trylock_read,
 333         .read_max = 2,
 334 };
 335
 336 static struct ast_custom_function unlock_function = {
 337         .name = "UNLOCK",
 338         .read = unlock_read,
 339         .read_max = 2,
 340 };
 341
 342 static int unload_module(void)
 343 {
 344         struct lock_frame *current;
 345
 346         /* Module flag */
 347         unloading = 1;
 348
 349         AST_LIST_LOCK(&locklist);
 350         while ((current = AST_LIST_REMOVE_HEAD(&locklist, entries))) {
 351                 /* If any locks are currently in use, then we cannot unload this module */
 352                 if (current->channel) {
 353                         /* Put it back */
 354                         AST_LIST_INSERT_HEAD(&locklist, current, entries);
 355                         AST_LIST_UNLOCK(&locklist);
 356                         unloading = 0;
 357                         return -1;
 358                 }
 359                 ast_mutex_destroy(&current->mutex);
 360                 ast_free(current);
 361         }
 362
 363         /* No locks left, unregister functions */
 364         ast_custom_function_unregister(&lock_function);
 365         ast_custom_function_unregister(&trylock_function);
 366         ast_custom_function_unregister(&unlock_function);
 367
 368         AST_LIST_UNLOCK(&locklist);
 369         return 0;
 370 }
 371
 372 static int load_module(void)
 373 {
 374         int res = ast_custom_function_register(&lock_function);
 375         res |= ast_custom_function_register(&trylock_function);
 376         res |= ast_custom_function_register(&unlock_function);
 377         return res;
 378 }
 379
 380 AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Dialplan mutexes");